1. Field of the Invention
The invention relates to a coolant dosing device of the liquid freezing system for cryogenic liquefied gas for producing low temperatures, for example in cryo-medicine.
2. Description of the Prior Art
Coolant dosing devices comprising a liquid freezing system are advantageous, because, during use, the gas consumption comes very close to the coolant demands required in theory. PCT 19958988.7 describes a coolant dosing device which, in an advantageous manner, by using small, gas-filled capsules offers very good mobility and is very efficient and practical in its handling.
However, the disadvantage of these dosing devices resides in the fact that their use is only possible in conjunction with commercially available capsules, because the gas inside the capsules contains, in part, substantial dirt particles. In addition thereto, the capsule needs to be pierced open mechanically by applying considerable force. This causes the formation of metal abrasion shavings having an increased negative impact on the existing filter.
Connecting the capsule to the dosing device must be done with the utmost care (with regard to the application force), if not, leakage may occur.
The sealing means in the region of the connecting zone are subject to extreme wear, since the capsule neck with its partially very rough surface properties is poorly suited for sealing. For physical and technical reasons the built-in filter in the coolant dosing device only offers a very small, effective filter surface. The accumulation of dirt particles at this location results in the so-called Joule Thomson effect when liquefied cryogenic gas is passing through. The coolant dosing device is consequently rendered useless, because micro-sized ice crystal particles, which are formed as a result of the Joule Thomson effect, clog the dispenser capillaries. Finally, when discharging the amount of residual gas, still present for technical reasons, in a gaseous state at the relatively high discharge velocity of the gas, additional, detaching dirt particles from the interior of the capsule impact negatively on the filter.